import java.util.*;

/**
 * Unit test for squid-0002: HttpHeader::removeConnectionHeaderEntries()
 * O(H * C) linear scan per response hop.
 *
 * Context: Called once per HTTP response in removeHopByHopEntries(), which runs
 * for every response forwarded by the proxy (client_side_reply.cc, Http1Server.cc).
 *
 * Defect: For each of H header entries, strListIsMember() scans all C tokens
 * in the Connection header string. Total: O(H * C) string comparisons per hop.
 *
 * Fix: Pre-build std::unordered_set from Connection tokens once (O(C)), then
 * probe O(1) per header entry. Total: O(C + H).
 *
 * At H=200 headers, C=50 Connection tokens: 10000 comparisons vs ~250 ops.
 */
public class SquidConnHeaderTest {

    // Defect: O(H * C) scan - strListIsMember called inside getEntry loop
    static int removeDefect(List<String> headers, List<String> connTokens) {
        int removed = 0;
        Iterator<String> it = headers.iterator();
        while (it.hasNext()) {
            String h = it.next();
            // strListIsMember: iterate all C tokens
            for (String token : connTokens) {
                if (h.equalsIgnoreCase(token)) {
                    it.remove();
                    removed++;
                    break;
                }
            }
        }
        return removed;
    }

    // Fix: O(C + H) - pre-build HashSet from Connection tokens
    static int removeFix(List<String> headers, List<String> connTokens) {
        // Build set once: O(C)
        Set<String> tokenSet = new HashSet<>();
        for (String t : connTokens)
            tokenSet.add(t.toLowerCase(Locale.ROOT));

        int removed = 0;
        Iterator<String> it = headers.iterator();
        while (it.hasNext()) {
            if (tokenSet.contains(it.next().toLowerCase(Locale.ROOT))) {
                it.remove();
                removed++;
            }
        }
        return removed;
    }

    static List<String> makeHeaders(int H, int matchCount) {
        List<String> h = new ArrayList<>();
        for (int i = 0; i < H - matchCount; i++)
            h.add("X-Custom-Header-" + i);
        for (int i = 0; i < matchCount; i++)
            h.add("conn-token-" + i);
        Collections.shuffle(h, new Random(42));
        return h;
    }

    static List<String> makeTokens(int C) {
        List<String> t = new ArrayList<>();
        for (int i = 0; i < C; i++)
            t.add("conn-token-" + i);
        return t;
    }

    public static void main(String[] args) {
        System.out.println("=== squid-0002: HttpHeader::removeConnectionHeaderEntries O(H*C) ===");
        System.out.println();

        // --- Correctness ---
        List<String> headers = Arrays.asList(
                "Content-Type", "Keep-Alive", "Transfer-Encoding",
                "Upgrade", "X-Custom", "Authorization", "Accept");
        List<String> connTokens = Arrays.asList("keep-alive", "upgrade", "transfer-encoding");

        List<String> dh = new ArrayList<>(headers);
        int dRemoved = removeDefect(dh, connTokens);

        List<String> fh = new ArrayList<>(headers);
        int fRemoved = removeFix(fh, connTokens);

        assert dRemoved == 3 : "defect: expected 3 removed, got " + dRemoved;
        assert fRemoved == 3 : "fix: expected 3 removed, got " + fRemoved;
        assert dh.equals(fh) : "result mismatch: " + dh + " vs " + fh;
        System.out.println("Correctness: PASS (both removed " + dRemoved + " hop-by-hop headers)");
        System.out.println();

        // --- Performance: adversarial case (H=200, C=50) ---
        int H = 200, C = 50, match = 20;
        int iters = 100_000;
        List<String> baseHeaders = makeHeaders(H, match);
        List<String> tokens      = makeTokens(C);

        // Warmup
        for (int i = 0; i < 5000; i++) {
            removeDefect(new ArrayList<>(baseHeaders), tokens);
            removeFix(new ArrayList<>(baseHeaders), tokens);
        }

        long t0 = System.nanoTime();
        int totalD = 0;
        for (int i = 0; i < iters; i++)
            totalD += removeDefect(new ArrayList<>(baseHeaders), tokens);
        long defectNs = System.nanoTime() - t0;

        long t1 = System.nanoTime();
        int totalF = 0;
        for (int i = 0; i < iters; i++)
            totalF += removeFix(new ArrayList<>(baseHeaders), tokens);
        long fixNs = System.nanoTime() - t1;

        assert totalD == totalF : "removed count mismatch: " + totalD + " vs " + totalF;

        double ratio = (double) defectNs / fixNs;
        System.out.printf("H=%d C=%d match=%d iters=%d%n", H, C, match, iters);
        System.out.printf("  defect: %,d ns total  (%,d ns/iter)%n", defectNs, defectNs / iters);
        System.out.printf("  fix:    %,d ns total  (%,d ns/iter)%n", fixNs,    fixNs    / iters);
        System.out.printf("  speedup: %.2fx%n%n", ratio);

        // At H=200, C=50 the defect does 200*50=10000 comparisons per call;
        // the fix does 50+200=250. Even with JVM overhead, expect >= 2x.
        assert ratio >= 2.0 :
            "Expected >= 2x speedup at H=" + H + " C=" + C + ", got " + ratio + "x";
        System.out.println("Performance: PASS");
        System.out.println("=== squid-0002 PASS ===");
    }
}